In order to get liquid nitrogen we need a little extra notice. Some experiments are:

Flowers can be frozen brittle
or fruit frozen solid so they will shatter when dropped. Another good demonstration
is to bounce a racquetball and then use liquid nitrogen to freeze it and shatter it.

Balloons of air can be
completely deflated and thrown on the floor to reinflate. If helium-filled
balloons are used, their volume will be reduced to about one quarter. They
are now denser than air and will drop to the floor, rising to the ceiling
after a few minutes as they warm up.

You can plunge your hand into
the liquid nitrogen for an instant. The Leidenfrost effect (vapor barrier)
protects your hand.

A piece of the new high
temperature superconductors will float a small magnet demonstrating the
Meissner effect after cooling in LN2. We also have a highly pinning superconductor
which will float over a magnet track, or even under the magnet track

Liquid nitrogen can be shown to freeze when the air is pumped out of a glass chamber as depicted in the video below.

The temperature coefficient of resistance can be investigated with a copper
wirewound resistor and a carbon resistor. A small circuit with a battery, lightbulb and
resistor is set up and then the resistor is put into a cup of liquid nitrogen. The change
light brightness indicates the sign of the temperature dependence.
The temperature dependence of a semiconductor can be investigated by dipping a large
green LED into liquid nitrogen and noting the color change.